colourvision v1.0
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1. Colour vision models have been extendent to accept any number of photoreceptor types (>=2).

2. Updated the trichromatic version of EMmodel, and the EMtriangle. The colour space is now built with a vector length = 0.75 to match the tetrahedron proposed by Endler and Mielke (2005). Doris Gomez derived a trichromatic version which is available in softaware AVICOL, and was previously implemented here (colouvision v0.1).

3. New function 'RNLthres' for colour thresholds based on receptor noise (Vorobyev and Osorio 1998).

4. 'RNLmodel' has a new argument ('R2') to be compared against R1 values (former 'R' argument).

5. Updated photon catch ('Q') calculation to give correct values when interval != 1. This change does not affect model results.

6. 'noise_e' function has been uptaded.

7. 'CTTKhexagon' and 'EMtriangle' are more flexible, and allow other arguments to be passed to the 'plot' function.

8. 'CTTKhexagon3D' and 'EMtetrahedron' are more flexible, and allow other arguments to be passed to the 'plot3d' function.

9. Fixed a bug in 'photor' when using 'beta.band=TRUE'.

10. Added 'methods' to 'plot' and 'plot3d' generics.